This invention relates to preparation of sintered articles. This invention, more specifically, relates to preparation of precursors, also known as green bodies, for such sintered articles. This invention, still more specifically relates to the preparation of dimensionally precise, complexly shaped, green bodies prepared from beta"-alumina precursor particulate and sacrifical binder.
Isostatic pressing of sinterable particulate solids is a known technique for preparation of sinterable articles not having complex configurations. For articles having complex shapes, e.g. flanges, isostatic pressing is unsuitable since it does not yield consistently desirable green bodies and sintered articles.
U.S. Pat. Nos. 4,158,688 and 4,158,689 to Pett et al, which are commonly assigned with this application, disclose preparation of green bodies of unusual dimensional precision using sacrificial binders similar to that of this invention. In these patents, the green bodies formed include compression molded cordierite ribbed sheets and extrusion molded beta"-alumina precursor particulate tubes. However, neither the binder composition used with the cordierite nor the extrusion composition used to make the tubes is optimal for use in compression molding of the beta"-alumina precursor particulate green bodies of the subject invention.
Particulate solids such as beta"-alumina ceramic precursor particulate have special properties inhibiting their facile shaping into dense, highly contoured sintered articles. As opposed to cordierite particulate solids, they are not as readily wetted by the binder ingredients. Furthermore, certain forms of such beta"-alumina precursor particulates inhibit the flow of sacrificial binder compositions containing them. Thus, in compression molding, there is a tendency of sacrificial binder compositions (containing sufficiently high amounts of particulate to prepare a dense ceramic) to resist flow into complex shapes or give articles with surface imperfections, if such a resistance to flow can be overcome.
This invention permits improvement in the compression molding of sacrificial binder compositions, densely packed with powdered beta"-alumina precursor particulate solids, into sound, dimensionally precise, complexly shaped green bodies.